We have continued our characterization of the novel hexasaccharide that is present in the urine of patients and female carriers of mucolipidosis IV. We now know that it is an unusual fucose-containing oligosaccharide. We shall determine its complete structure and attempt to learn its metabolic origin. We have found that these patients are achlorhydric and that they have elevated levels of gastrin in their sera. Pareital cells that are responsible for acid secretion have a distorted morphology in biopsies obtained from patients with mucolipidosis IV. We believe these abnormalities contribute to the etiology of mucolipidosis IV, and we are trying to elucidate the specific biochemical lesion in this hereditary disorder.